Tritium is a radioactive isotope of hydrogen with an atomic mass of three, a half life of 12.3 years and decays to stable helium-3 with the emission of an electron. Production of tritium by man occurs from basically two sources neutron irradiation of lithium and the capture of neutrons by deuterium in heavy-water. The primary source of tritium is associated with heavy-water reactors; however, bombarding of experimental gas cooled lithium targets with a neutron beam can also release small amounts of tritium. For the safety of reactor operating personnel and others who might come into contact with tritium, it is necessary to be able to monitor and collect the tritium produced.
Small amounts of tritium, in its gaseous state, are often mixed with fractional percent levels of hydrogen to facilitate its transfer through the respective piping used in its measurement and collection. Tritium, a weak beta emitter, is often present in small amounts in combination with other radioactive gases which emit both beta and gamma radiation. This combination together with the several possible chemical forms of tritium can make tritium difficult to measure. Most tritium monitoring systems rely on the use of an ion chamber that is nondiscriminating with respect to the form of ionizing radiation present in measuring the radioactivity of the gas sample; the ion chamber method of measurement results in both beta and gamma emitters combining to give a total result rather than supplying a reading for tritium alone as a single beta emitter. There are some commercially available devices which are capable of determining the radioactivity of the tritium alone from a gas stream; these generally involve the use of a dual ion chamber. With the dual ion chamber, the gas stream goes through one of the ion chambers that sees all of the radiations and a second chamber which is isolated from the gas flow and sees only the penetrating gamma-rays. The activity of the second chamber is then subtracted from the total activity recorded by the first chamber and the remainder is the tritium concentration provided that there are no other beta emitters. There are inherent problems associated with this technique because in some cases the gamma and beta emissions may be detectable by the total chamber and not be accounted for in the second or compensation chamber. Also, these tritium measuring devices function best at high concentrations of tritium and do not perform as well at low tritium concentrations.
Tritium collection is generally accomplished through the use of an oxidation process where the tritium is oxidized to tritiated water which is then trapped on silica gel or some other absorbent. This method precludes or greatly encumbers on-line analysis of the tritium activity as opposed to a system which employ zirconium alloy getters to collect, concentrate, and purify the tritium and provides a means of greatly improving on-line collection and provides the capability for on-line tritium monitoring.
In the case where a helium-argon gas mixture is used to stabilize the temperature of a lithium target subject to neutron bombardment, a small amount of tritium together with a large amount of gamma producing argon is formed. In order to measure the tritium activity, it is necessary to physically separate the argon from the tritium since the ratio of the tritium to the argon is often of the order of 10.sup.-7. There is no known device currently able to accomplish the separation of tritium from a radioactive or nonradioactive inert gas stream, collect the tritium, and measure the quantity of tritium and to further accomplish this under computer control so as to provide a system for long term collection and analysis of the tritium.
Therefore, it is an object of this invention to provide an apparatus to collect and measure the tritium from a flowing inert gas stream.
It is another object of this invention to purify the gas to the degree that all tritium molecular species will be converted to an elementary pure gas containing only the isotopes of hydrogen.
It is another object of this invention to interface a computer and software system with the collecting and measuring hardware to provide for automatic control of the system.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.